LONDON (AP) -- British Prime Minister Theresa May's brief summer holiday from Brexit battles came to a noisy end Monday, as she faced attack from both sides of her divided Conservative Party.
Archrival Boris Johnson inflamed speculation that he aims to oust May by branding her plan for Brexit "a disaster."
Johnson fumed in a newspaper column that May's proposal to retain close economic ties with the European Union after Brexit would leave Britain locked in the trunk of a Brussels-driven car with "no say on the destination."
Meanwhile, a more pro-EU Conservative faction argued that the U.K. should keep even closer bonds with the bloc than May is proposing, at least temporarily.
Lawmaker Damian Green, an ally of May, conceded the prime minister was in a tight spot.
"The government is walking a narrow path with people chucking rocks from both sides," he told the BBC.
Johnson, who resigned as foreign secretary in July after feuding with May over Brexit, used his weekly column in the Daily Telegraph newspaper to accuse May of surrendering to the EU in divorce negotiations.
Johnson said that Britain has "gone into battle with the white flag fluttering over our leading tank" and had agreed to pay a 40-billion pound ($51 billion) divorce bill in return "for two-thirds of diddly squat."
Britain is due to leave the EU in March, but negotiations have stalled amid divisions within May's Conservative government over how close an economic relationship to seek with EU.
A proposal hammered out by May's Cabinet in July at the prime minister's Chequers country retreat proposes keeping the U.K. aligned to EU regulations in return for free trade in goods. The plan infuriated Brexit-backers including Johnson, who quit the government in protest. Johnson claims the Chequers plan would prevent the U.K. from striking new trade deals around the world.
"We will remain in the EU taxi; but this time locked in the boot (trunk), with absolutely no say on the destination," Johnson wrote. "We won't have taken back control -- we will have lost control."
May's official spokesman, James Slack, dismissed Johnson's attack, saying there were "no new ideas in this article to respond to."
"What we need at this time is serious leadership with a serious plan and that's exactly what the country has with this prime minister and this Brexit plan," he said.
With Parliament due to return Tuesday from its summer break, Johnson and his fellow Brexit enthusiasts aren't the only obstacle May faces as she tries to get her Brexit deal past her Conservative Party, Britain's Parliament and the EU.
On Monday, Conservative supporters of "soft Brexit" put forward a rival proposal, arguing that Britain should stay in the EU's single market for goods and services for three years after Brexit while it negotiates a future free trade deal with the bloc -- a plan summed up as "Norway, then Canada," in reference to those countries' trade relations with the EU.
Conservative lawmaker Nick Boles said the idea was better than the Chequers proposal, which had "close to zero" chance of being approved by Parliament.
"What I want is a plan that's workable," Boles told the BBC. "We can't get to Nirvana in one step."
Meanwhile, pro-EU campaigners are pushing for a new referendum on any deal agreed between Britain and the EU. May insists that won't happen, but the idea is gaining momentum.
Britain and the EU had hoped to hammer out an agreement on divorce terms and the outlines of future trade by a European Council summit in October so that it can be approved by individual EU countries before the U.K. leaves the bloc on March 29. Both sides now say that deadline may slip to November or later.
The Chequers plan has been received coolly by EU leaders, who warn that Britain can't "cherry pick" aspects of membership in the bloc without the full cost and responsibilities.
The EU's chief Brexit negotiator, Michel Barnier, told German newspaper Frankfurter Allgemeine Zeitung that the bloc has "a coherent market for goods, services, capital and people -- our own ecosystem that has grown over decades. You cannot play with it by picking pieces."
The British government insists it's confident of reaching an agreement with the EU, but is preparing for all outcomes, including a "no deal" Brexit.
Think tank U.K. in a Changing Europe said Monday that the short-term consequences of failing to get a deal would be "severe and overwhelmingly negative."
In a report, it said a "chaotic Brexit" would mean "the disappearance without replacement of many of the rules underpinning the U.K.'s economic and regulatory structure" would disrupt everything from agriculture to financial services to aviation.